Abstract: In hydrochloric acid medium, 12-tungstophosphoric acid(TP) reacts with some local anesthetics such as tetracaine(TC), procaine(PC) and lidocaine(LC) to form ion-associate complexes, resulting in a significant enhancement of resonance Rayleigh scattering(RRS) and appearance of new RRS spectra. Their maximum scattering peaks were at 345 nm(TP-TC), 368 nm(TP-PC), 379 nm(TP-LC), and the RRS intensities are proportional to the concentrations of the three local anesthetics in a certain range. Therefore, a novel method for the determination of TC, PC and LC by RRS coupled with flow injection analysis(FIA) was deve-loped, and the detection limits(3σ) were 0.5—9.5 ng/mL for different local anesthetics. Taking the TC-TP system with the highest sensitivity as an example, the effects of coexisting substances and analytical application were studied. The results show that the method has good selectivity and reproducibility. The recovery of the present method applied to the determination of TC in urine sample was 98.8%—103.2%. And the relative standard derivation for 9 successive determinations of 2.0 μg/mL TC was 1.7% with sampling frequency of 60 h^-1. In addition, the charge distribution of three anesthetics was calculated by quantum chemistry AM1 method, and the reaction mechanism was discussed from the difference of the anesthetics structure.

Key words: 12-Tungstophosphoric acid, Resonance rayleigh scattering, Flow injection, Local anesthetic